1. Field of the Invention
The present invention relates to a communication system, especially to a transmission medium testing apparatus and method applying to a communication system.
2. Description of the Prior Art
In communication system, a transmission medium is used to transmit signals from one endpoint to a remote endpoint. The condition of the transmission medium, such as the length of the cable, whether a short circuit, an open circuit, or an impedance-mismatching point in the cable, all significantly influences the quality of the transmitted signal. Therefore, transmission medium testing apparatuses and methods are used to detect the condition of the transmission medium in the communication system.
Please refer to FIG. 1A, FIG. 1B, and FIG. 1C; FIG. 1A to 1C show the schematic diagrams of the cable testing method in the prior art. The method for testing a cable in the prior art is to transmit a pulse wave from endpoint A; if the cable is in good condition, the pulse wave/transmitting wave will be transmitted from endpoint A to endpoint B, as shown in FIG. 1A. If the cable has an impedance-mismatching point C, such as short circuit or open circuit, the pulse wave/transmitting wave produces a reflected wave from endpoint C back to endpoint A, as shown in FIG. 1B. The time spent by the detected reflected wave to reach endpoint A depends on the location of the impedance-mismatching point C, and the impedance mismatching condition of the impedance-mismatching point C depends on the characteristics of the reflected wave (such as: the phase). Therefore, the method for testing a cable in the prior art is to transmit a signal from endpoint A, and the time spent by the detected reflected wave to reach endpoint A and the dimension of the reflected wave are used to determine the location and the condition of the impedance-mismatching point on the cable.
The cable testing method in the prior art described above can only be applied in a half-duplex communication system. If a full-duplex network system is used, such as 1000 Mbps Ethernet, when endpoint A transmits a pulse wave, the endpoint B also transmits a signal to endpoint A. Therefore, while cable testing is being performed, the endpoint A will receive both the reflected wave caused by the impedance-mismatching point C and the transmitting wave transmitted from endpoint B, as shown in FIG. 1C. Furthermore, when the transmitting end (Tx) of the full-duplex network system transmits signals, the transmitted signal will generate an echo effect at the receiving end (Rx). Therefore, the full-duplex network system cannot determine the location and the condition of the impedance-mismatching point on the cable from the signal received at endpoint A. Consequently, the method using the reflected wave to test cable in the prior art cannot be used in the full-duplex network system, meaning the application of the prior art is limited.
Therefore, the main objective of the present invention is to provide a transmission medium testing apparatus and method to solve the problems described above.